Prosecutors said the men are being charged in absentia with conspiracy to murder, attempted murder and use of the nerve agent Novichok.

Prime Minister Theresa May said the two men are officers of Russia’s GRU military intelligence service.

May spoke by phone with Canadian Prime Minister Justin Trudeau following her statement to the Commons on Wednesday, said the PM’s official spokesman.

The spokesman said: “They agreed that the UK and Canada will continue to work closely together to confront the threat which Russia poses to the international rules-based system.”

May is expected to speak to other leaders of Britain’s allies over the next few days, but is not seeking a conversation with Vladimir Putin, said the spokesman.

UK Security Minister Ben Wallace has said the Russian President bears ultimate responsibility for the Salisbury Novichok attack because “it is his government that controls, funds and directs” the GRU intelligence service blamed for the nerve agent poisoning